Thinking about it... What I find incredulous is that a braincrab on Unnamed Lava Generica World nails the doctor, and then five more just materialize on Earth, nailing four random blokes and the most important person in the Doctor's life, the Impossible Girl. That's why I kind of think it would've been better if it had just been the one brain-crab, and the psychic power of the Doctor was enough to reach across all of time and space.
That said, I did think there was a certain... Poignancy to the bit where it starts to come out that the braincrabs generate fantasies within fantasies, and since it's Christmas Eve, everyone's mind would go straight to Santa Claus.
Everyone's mind, that is, except for a select few people who hear a certain grinding whirr and a gong. That's when I began to believe, erroneously, but plausibly, that the Doctor wasn't even in the brain-simulation at all, but was a mental construct entirely of Clara's; her mind would reject Father Christmas as someone come to help her, after all, she'd start to question it, question him, think analytically about him... But who would she never, *ever* question, no matter how ridiculous or implausible it would be that he'd turned up? Who would she listen to, even obey, if showed up and started talking gravely, giving her an urgent, direct imperative to not question a thing and do what he said?
The Doctor. Kind of like Pond's unbreakable faith in the Raggedy Man - faith which, ironically and paradoxically, turned out to be completely justified, even when he had to shatter that faith entirely in order to save her.
So, what're the possibilities that they're still sucking down a faceful of alien wing-wong and the entire next season will be a dream? I hope not, 'cause that would be bollocks, especially with how much I enjoyed seeing "The Doctor and Clara will return" at the end.
Also, I kind of wish her title would come up more, along with The Oncoming Storm for the Doctor. I mean, let's face it, they're basically the ultimate guile heroes. So much so that the Dalek Empire had an epithet just for him, and that's not the kind of epithet that a fellow gets lightly.